While olefin polymers are widely and commonly used as molding materials for various articles, the characteristics required depend on the end use and the molding method employed. For example, olefin polymers having a narrow molecular weight distribution and a relatively low molecular weight are suitable for injection molding, and those having a broad molecular weight distribution and a relatively high molecular weight are suitable for blown-film extrusion or blow molding. In particular, for the purpose of maintaining bubble stability on high-speed blown-film extrusion, preventing drawdown in parison in blow molding especially for production of large-sized containers, and maintaining uniform ductility in blow molding for production of articles having a complicated shape, it is necessary to choose an olefin polymer having a high melt tension and a high melt elasticity (die swell ratio).
However, attempts to obtain an olefin polymer having improved melt tension or melt elasticity while exhibiting broadened molecular weight distribution often encounter difficulty in maintaining satisfactory productivity. For example, JP-A-52-24292 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") proposes a process for producing an olefin polymer having a broad molecular weight distribution, a high melt tension, and a high die swell ratio. While this process achieves an improvement in die swell, the improvement attained is in a range that is not always sufficient for maintaining high productivity. Moreover, the process is disadvantageous because fish eyes cannot be avoided without powerful kneading beforehand.